The present invention relates to a connecting rod bearing, consisting of a pair of semi-cylindrical bearings, for an internal combustion engine, for rotatably supporting a crankpin which connects a connecting rod and a crankshaft to each other, wherein lubricant oil is supplied to an inner surface of the connecting rod bearing, the lubricant oil being supplied at first to an inner surface of a main bearing which supports a crankshaft, and caused to flow in an inner lubricant oil passage formed in the crankshaft toward the inner surface of the connecting rod bearing.
In the internal combustion engine, the crankshaft is supported, at its journal portion, in a lower section of an engine cylinder block through a main bearing consisting of a pair of semi-cylindrical bearings. With regard to the main bearing, the lubricant oil discharged from an oil pump is supplied into a lubricant oil groove, which is formed on the inner surface of the main bearing, from an oil gallery formed in the wall of the cylinder block through a through-hole formed in the wall of the main bearing. The journal portion is provided with a first lubricant oil passage formed through diametrically in the journal portion, which passage is in fluid communication with the lubricant oil groove via opposite end openings of the first lubricant oil passage. Further, a second lubricant oil passage is formed in the journal portion and a crank arm portion, branching from the first lubricant oil passage diametrically formed in the journal part. The second lubricant oil passage is in fluid communication with a third lubricant oil passage formed diametrically through a crankpin. Thus, the lubricant oil, which is supplied into the lubricant oil grooves formed on the inner surface of the main bearing from the oil gallery formed in the wall of the cylinder block through the through hole formed in the wall of the main bearing, is supplied into a clearance between sliding surfaces of the crankpin and the connecting rod bearing from an outlet port at an end part of the third lubricant oil passage through the first to third oil passages.
The lubricant oil, which is fed from the engine cylinder block into the connecting rod bearing through the journal portion, may be accompanied with foreign substances existing ab ovo in lubricant oil passages in the pertinent members. Should the foreign substances accompanied in the lubricant oil be fed into a clearance between sliding surfaces of the crankpin and the connecting rod bearing, there is a risk that the sliding surface of the connecting rod bearing may be damaged. It has been believed that the foreign substances having entered into the clearance between the sliding surfaces of the crankpin and the connecting rod bearing should be immediately discharged from the clearance.
As a countermeasure against the foreign substances accompanied in the lubricant oil, there has been proposed a way of discharging the foreign substances accompanied in the lubricant oil from the main bearing which supports the journal portion of the crank shaft and which consists of a pair of semi-cylindrical bearings, wherein one of the semi-cylindrical bearings is provided with an axial groove along its circumferential ends on the inner surface side of the semi-cylindrical bearing, and which has a through hole adapted to directly receive the lubricant oil supplied from an oil gallery formed in the cylinder block wall, so as to be in fluid communication with a circumferential lubricant oil groove formed on the inner surface throughout the circumferential length of the semi-cylindrical bearing and connected to the through hole (cf. JP-A-8-277831 and JP-A-2005-69283).
Consideration with the abovementioned proposal:
While the crank shaft is provided, as set forth above, with the second lubricant oil passage branched off from the first lubricant oil passage diametrically formed in the journal portion of the crank shaft, and passing through the crank arm portion, wherein the second lubricant oil passage is in fluid communication with the third lubricant oil passage which is formed diametrically in the crankpin, there may remain large burrs, each having an extended planar shape consisting of a metal of the crank shaft (usually steel), in a connecting part (i.e. a crossing part) between the first and second oil passages and in the connecting part (i.e. a crossing part) between the second lubricant oil passage and the third lubricant oil passage formed in the crankshaft, since the first, second and third lubricant oil passages are formed by drilling. Should the burrs be sheared by the lubricant oil stream during operation of an internal combustion engine, the burrs are accompanied in the oil stream and fed to an outlet port of the third lubricant oil passage which outlet port is located at the surface of the crankpin. If the size of the burrs is larger than that of the clearance between the inner surface of the connecting rod bearing and the crankpin, the burrs remain at the position of the outlet port of the third lubricant oil passage at the surface of the crankpin since they cannot enter into the bearing clearance, thereby damaging the inner surface of the connecting rod bearing while the burrs are dragged relative to the connecting rod bearing in the bearing clearance between the connecting rod bearing and the rotating crankpin. In this case, the dragging is continued until the burrs become smaller in size so as to be able to enter into the bearing clearance after the burrs have been sheared by a shear force acting thereon, thereby the inner surface of the connecting rod bearing is seriously damaged.
Thus, when intending to apply the idea of the above proposal into the connecting rod bearing, it will be needed to form the axial grooves having a very large sectional area along the circumferential ends on the inner surface side of the semi-cylindrical connecting rod bearing in order to cause the large size foreign substances accompanied in the lubricant oil to discharged from the inner surface of the bearing.
However, these years, in internal combustion engines, efforts have been made for the purpose of making oil pumps for the lubricant oil smaller in size in order to lower the fuel consumption, thereby the supply quantity of the lubricant oil onto the sliding surface of a bearing has been decreased as compared with old type internal combustion engines. Thus, should the axial groove be provided with a large sectional area in order to discharge the foreign substances, as in the above proposal, the leakage amount of the lubricant oil will increase resulting in an insufficient supply of the lubricant oil onto the sliding surface of the bearing.